Mucopolysaccharidoses et oligosaccharidoses

The mucopolysaccharidoses (MPS) are a group of inherited metabolic disorders caused by a deficiency of specific lysosomal enzymes. The enzyme deficiency results in interference with cellular function because of excess accumulation within the cells of partially degraded glycosaminoglycans (GAG), which are also excreted in excess in the urine of affected patients. The ubiquitous nature of GAG within the connective tissue of the body results in a wide range of clinical effects. The type of GAG stored depends on the specific enzyme deficiency and classification of the disorders is now based upon these deficiencies, rather than clinical features. Currently, MPS is classified into various types (I to VII), and additional diseases (oligosaccharidoses) are recognized (GM1 gangliosidosis, mannosidosis, fucosidosis, aspartylglucosaminuria), some of which are mucolipidoses (sialidosis, I cell disease, pseudo-Hurler’s polydystrophy) which demonstrate similar clinical and radiologic findings. Common to the MPS types and the mucolipidoses are certain clinical and radiographic characteristics ; the radiographic abnormalities are designated dysostosis multiplex.